A deflector of the kind described in the specification of U.S. patent application Ser. No. 253,864, filed Oct. 5, 1988, and the corresponding published French patent application No. FR 2 621 288A, comprises a profiled portion having a first zone which is substantially flat and which extends backwardly from a leading edge, the said first zone being slightly inclined with respect to the mean plane of the surface to be swept, and a second zone adjacent to the first zone but inclined to the swept surface at a greater angle than the first zone. The profiled portion lies at a sufficiently small distance away from the surface to create a ground effect which produces a relatively large reduction in pressure below the deflector, that is to say in the zone lying between the swept surface and the profiled portion of the deflector, and this enables the wiper blade to be applied correctly against the swept surface.
It has been proposed to mount this type of air deflector on either the wiper blades or the wiper arms, in such a way that during the wiping operation on an inclined windshield, while the automotive vehicle is moving, wiping is facilitated during upward movement of the wiper arm. This is achieved by arranging that the air flow, impinging on the deflector, urges the windshield wiper blade in the same direction as does the drive motor of the wiper, while during downward movement of the arm, the speed of descent of the wiper blade remains substantially equal to the speed of its upward movement.
In order to achieve this, there must be no perturbation or turbulence, such as a possible modification of the pressure drop underneath the deflector, which would hamper good functioning of the deflector.